Credit: Cole Brookson | Microplastics collected in the San Francisco Bay Area are identified and labeled accordingly for an ongoing study in a lab headed by Chelsea Rochman, an assistant professor at the University of Toronto.
About 8 million metric tons of waste plastic enters the oceans every year. Over time, these bottles and bags break down into particles that are micrometers or even nanometers in size. Researchers are accumulating evidence showing that these particles are being consumed not only by birds and fish but by humans, too. With the public spotlight on plastic waste, regulators and industry are now funding studies to determine the risks that microplastics pose to the food chain and, ultimately, human health. But analyzing microplastics is highly complex. Analytical chemists are developing novel techniques and study protocols to fill the many data gaps.
About a year ago, Philipp Schwabl, a research scientist and physician specializing in intestinal diseases at the Medical University of Vienna, read an article about plastic pollution and started to connect the dots.
About 8 million metric tons of plastic waste enters the oceans every year; eventually those bottles and bags break down into particles. Schwabl wondered whether tiny plastic particles—known as microplastics—are entering the food chain and being consumed by people and, if so, whether they could harm cells and tissue in the human gut.
Schwabl could find no definitive answers, so he decided to undertake his own study. Serendipitously, he discovered that Bettina Liebmann, an analytical chemist who heads Environment Agency Austria’s effort to analyze microplastics, was based a few minutes’ bicycle ride away. The pair teamed up and in October 2018 released the outline of a small pilot study, now undergoing peer review, that they say is the world’s first to confirm that humans are consuming microplastics. In the study, the researchers identify a variety of common plastics in eight subjects’ stool. Because of the study’s small size, the researchers say they are now looking to undertake a bigger study using a larger population.
At about the same time that Schwabl was reading up on microplastics, public interest in plastic pollution erupted, thanks in part to the airing of a BBC documentary on ocean plastics. It was followed by a series of scientific studies adding to the body of evidence that seabirds and aquatic animals—including fish species eaten by humans—often consume microplastics.
But as Schwabl has discovered, showing definitively that people are eating plastics is one thing, but determining whether they hurt humans is tricky, partly because not all microplastics pose equal risks: The tiny particles are highly variable in size, shape, and chemistry and are found in different concentrations in the environment. In addition, potential hazards presented by microplastics may come from the polymer itself, property-enhancing polymer additives, contaminants that particles have absorbed in the environment, and bacteria that they carry on their surfaces. Isolating exposure to microplastics from food versus the air is another challenge.
In a bid to discover whether microplastics pose a risk to human health, organizations around the world—many of them in Europe—are now funding research projects to determine their fate and impact. While some scientists contend that consumption of microplastics from fish and other food poses little or no risk to human health, others say that more analysis is needed and that microplastics could harm the human gut and other organs. Much is riding on the research’s findings.
Last month, Science Advice for Policy by European Academies (SAPEA), a European advisory body, published a 173-page meta-analysis of existing studies concluding that microplastics do not pose a widespread risk to the environment and human health. The analysis finds only isolated locations around the globe where concentrations of microplastics in sediments and water are so high that they could present a concern to human health.
“Of course, a lack of evidence for risk does not mean we should assume there is no risk,” says Bart Koelmans, chair of the working group that created the report. The group acknowledges that its conclusions are based on a series of assumptions. Measurement methods currently available have limitations, and there is a “need for more inquiry,” the SAPEA report states.
Ominously, SAPEA also concludes that the situation could change if pollution continues at the current rate. It cites one study concluding that risks posed by microplastics could become widespread by 2060.
Heather A. Leslie, a toxicologist and expert in microplastics with Vrije Universiteit Amsterdam, is concerned that widespread effects could already be happening. Microplastics could be causing chronic inflammation, which she describes as a “silent killer because it can be a prequel to other diseases,” in people’s tissues. Further investigation is warranted, she says. Some insight into the possible physical effects of plastic particles can be gleaned from animal models and lab tests of human cells and tissues.
They include lung and gut injury, according to a study by Leslie and A. Dick Vethaak, a professor at the Dutch research institute Deltares (Environ. Sci. Technol. 2016, DOI: 10.1021/acs.est.6b02569).
To go deeper, researchers say, a good starting point is looking at food sources that may be high in microplastics.
In April 2018 at Analytica, a conference and trade show for analytical chemists held in Munich, Leslie suggested that shellfish could be the “canary in the coal mine” when looking at the effect of microplastics on organisms because shellfish concentrate particles—including those made from plastic—by filtering them from water.
A lab study led by the University of Plymouth published late last year in Environmental Science and Technologyappears to add credence to Leslie’s hypothesis (2018, DOI: 10.1021/acs.est.8b05266).
In the study, funded by the UK’s Natural Environment Research Council, scallops—a shellfish species found on many restaurant menus—were found to accumulate billions of nanoplastic particles in their tissues within just a few hours of being exposed to them at a concentration similar to those in the oceans. Nanoplastics are extremely small microplastic particles that are below 100 nm in size. The authors say it is the first time that a study of its kind has used a concentration of nanoplastics similar to those found in the environment.
“The scallops were destroyed at the end of the experiment, but nanoplastic in seafood could easily be eaten by humans; there is no reason to doubt this is happening,” says Richard C. Thompson, a professor of marine biology at the University of Plymouth and one of the study’s contributors.
Whether this phenomenon translates into a health risk, though, is something of a leap, according to Thompson. “I don’t see any evidence at present of concern for human health in eating seafood,” he says.
SAPEA concurs with Thompson, asserting that shellfish pose no major human health risk. SAPEA draws its conclusion by comparing the amount of plastic people might consume from shellfish with their expected total environmental exposure. For example, one portion of mussels would contribute less than 2% per day of a person’s exposure to bisphenol A, a monomer used to make polycarbonate plastic, the report says.
But MedUni Vienna’s Schwabl is among a number of scientists who are more skeptical about the risks posed by microplastics that might be taken up by the body. “Now that we have first evidence for microplastics being ingested and excreted by humans, we need further research to understand if there is also microplastic uptake and if this potentially affects human health,” he says.
Schwabl wants to investigate whether there is a link between microplastics and gastrointestinal disease. “Patients with a damaged gut barrier are more susceptible to uptake of microparticles,” he claims.
And the risk could go beyond the gut. “In animal studies, the smallest microplastic particles are capable of entering the bloodstream and lymphatic system and may even reach the liver,” Schwabl says.
He hopes to raise hundreds of thousands of dollars to fund a second, more detailed version of his initial study to evaluate the effect of microplastics on individual cells. Such a study could determine whether cells can be damaged by exposure to certain microplastics, Schwabl says. While his initial research featured just eight subjects, a subsequent study would investigate a much larger human population.
▸ What they are: Plastic fragments between 100 nm and 5 mm in size.
▸ How they form: Most microplastics result from the environment shredding littered plastics over time. They are also intentionally placed in paints and cosmetics.
▸ The scale of the problem: About 8 million metric tons of plastic enters the aquatic environment every year, but microplastics are also in the air, the soil, and our homes.
Potential hazards from microplastics
▸ Human pathogens: Bacteria such as Escherichia coli have been discovered on the surface of microplastics.
▸ Chemicals from the environment: Synthetic hydrophobic contaminants in oceans can adsorb to the surface of microplastics.
▸ Toxic monomers or additives: Chemicals such as bisphenol A, used to make polycarbonate, are endocrine disruptors.
▸ Physical obstruction: Large pieces of plastic can cause obstruction in animals’ guts.
New tools for analyzing microplastics
▸ Pretreatment: Improved technologies for isolating microplastics in wastewater harness chemicals and enzymes.
▸ Tagging: Radiolabeling of microplastic particles can identify whether they are consumed by shellfish and other animals.
▸ Standards: Standard operating procedures and method validation for lab testing of microplastics, along with improved reference materials, allow researchers to compare results.
Schwabl won’t just be repeating the first study but will investigate whether plastic gets taken up into the body from the gut and harms the intestinal tract or whether it simply passes through to the stool.
While some of the microplastics identified in the Schwabl-Liebmann study may have come from fish, the study included two non-fish-eating participants who had plastics in their stool. One possible source is food packaging.
People could also be consuming plastic particles, including those added intentionally to cosmetics and paints, from sewage used by farms. Approximately 43% of microplastics that enter wastewater treatment plants end up on agricultural land as part of fertilizers made from treated sewage sludge, according to Peter Simpson, senior scientific officer at the European Chemicals Agency (ECHA), the body responsible for regulating chemicals in the European Union.
“Their accumulation in agricultural land is a concern because we cannot currently assess the risks to the environment resulting from such long-term accumulation and exposure,” Simpson says.
The use of microbeads in cosmetics was banned in the US in July 2018, and Europe is expected to introduce a similar ban starting in 2020. ECHA says this would prevent almost 30,000 metric tons of microplastics per year from entering the environment.
ECHA, as well as the European Food Safety Authority, will draw on guidance from the European Commission’s Joint Research Centre, a research institute that seeks to develop, harmonize, and support standardization of analytical methods for assessing microplastics.
A hotbed of European microplastic analysis is Germany’s Ministry of Education and Research, which is funding 18 projects on plastics in the environment. Some of them are investigating the fate of microplastics, including particles from vehicle tires, or are developing tools for evaluating the toxicity of microplastics.
Such studies are needed to get a clearer picture of the risks that microplastics pose in the food chain, according to a number of experts in the field. “We know more about exposures, and there is no doubt we are exposed. But we still know little about whether there are effects,” says Chelsea Rochman, assistant professor in the Department of Ecology and Evolutionary Biology at the University of Toronto.
Rochman led a 2015 study showing that microplastics were present in a substantial percentage of fish sold in Indonesia and California. Since then, she says, researchers have come no closer to determining the risks that microplastics pose to humans.
Some scientists warn that when eaten, microplastics can deliver component or contaminant chemicals in a way that is more harmful than if those same chemicals were inhaled.
“Because chemicals associated with microplastics are being delivered on a different chemical basis to the tissue, it could mean that they have a higher bioavailability,” says David Santillo, senior scientist at Greenpeace’s global analytical chemistry lab, which is based at the University of Exeter. “As a result, they should be investigated separately.”
Among the potential hazards posed by microplastics, endocrine disruption and exposure to pathogens are two that are little understood, Santillo says. Endocrine-disrupting substances, such as bisphenol A, could cause effects at extremely low levels of exposure if concentrated on or within microplastic particles, Santillo says.
Meanwhile, plastic debris in rivers and lakes has been shown to contain the human pathogens Escherichia coli, Bacillus cereus, and Stenotrophomonas maltophilia (Environ. Sci. Technol. 2014, DOI: 10.1021/es503610r).
The potential risks posed by microplastics are starting to attract the chemical industry’s attention. The International Council of Chemical Associations (ICCA), a trade group, has set up a microplastics task force. Chemical industry executives say they are keen to determine the best ways of evaluating the risk that microplastics pose to human health and the environment.
“We do not only need more data; we need suitable data,” says Philipp Hopp, an ICCA task force member and ecotoxicologist at BASF.
A whole host of standard practices needs to be agreed upon, Hopp says. These practices include methodologies, risk approaches, exposure modeling to properly assess hazard, lab-to-field extrapolations, and more, he says.
The ICCA task force held a symposium on the issue in 2018 and is planning a technical workshop in Europe later this year to bring experts together. “We can learn a lot from nanomaterial research; however, microplastic particles possess many unique features which have to be considered and investigated,” Hopp says.
As a member of ICCA, Cefic, Europe’s leading chemical industry association, has set aside about €650,000 ($680,000) for two studies: one to determine microplastic hazards and one to develop a model of how microplastics are transported in the aquatic environment and where they end up. Via its Long-Range Research Initiative (LRI), Cefic has contracted out the two studies to independent research organizations. Both are due to get underway by March 31.
In an indication that scientists have an appetite to investigate microplastics, the LRI program received three times the usual number of applications to undertake the studies, says Bruno Hubesch, head of LRI.
Less clear is whether overall funding matches researcher interest in studying the risks posed by microplastics. According to the University of Plymouth’s Thompson, there is “no particular uplift” in funding. He says he’s “concerned we need more science to help identify the best solutions.”
It is a point echoed by Greenpeace’s Santillo. “Microplastics have been an overlooked and underinvestigated source of chemical contamination,” he says.
Scientists across the board take the position that consumers should continue to eat shellfish and other fish even if—as we now know—they are likely to contain microplastics. “The most important thing at the moment is really not to worry or be frightened about this. We are far from calling microplastics a danger,” Schwabl says.
They also agree that the analysis is far from complete. As Leslie said at the Munich meeting, “We are still at the initial stages of understanding human exposure and what the threat may be.”
To determine the risk that microplastics may pose to human health, researchers are devising a host of novel approaches and analytical techniques. There is also a surge of activity around the world by scientists, regulators, and instrument makers to harmonize and validate the best analytical methods so that studies can be directly compared. New techniques are required because of the complexity associated with analyzing microplastics.
Philipp Schwabl, a research scientist and physician specializing in intestinal diseases at the Medical University of Vienna, and Bettina Liebmann, an analytical chemist who heads the Environment Agency Austria’s effort to analyze microplastics, conducted a small study to determine whether people are consuming microplastics. They drew on novel techniques to assess the stool of eight people located around the world. None of the participants were vegetarians; six of them consumed seafood.
In the study, the scientists identified up to nine different plastics sized between 50 and 500 µm in every stool sample, with polypropylene and poly(ethylene terephthalate) being the most common. On average, the researchers found 20 particles per 10 g of stool.
Liebmann adapted techniques used by the Environment Agency Austria for analyzing microplastics in wastewater. One of them involved applying a combination of chemicals and enzymes to the stool to remove organic matter and retain plastic particles. “We continue to broaden our toolbox of methods,” she says.
Liebmann then combined Fourier transform infrared spectroscopy (FT-IR) with microscopy and imaging to identify various plastic particles. Each plastic type absorbs light of characteristic wavelength, allowing researchers to create a database for material identification. “The acquired FT-IR spectra can be compared against the database to determine which plastics are present,” Liebmann says. With the technique, stool that is put on a 47 mm diameter filter can be scanned in about 8 h, generating about 1 GB of data.
The technique, which can measure particles from 500 µm down to a few micrometers, allows Liebmann to determine whether a microplastic particle is a fiber or fragment by measuring its diameter. “We would need a different approach for measuring nanoscale,” she says.
Methods used by the University of Plymouth’s Maya Al Sid Cheikh and colleagues to determine the uptake of nanoplastics by scallops also required new techniques. Before the study, no analytical techniques had yet been applied that were sensitive enough to measure the distribution of microplastics in wild organisms, according to Al Sid Cheikh. So the Plymouth researchers developed their own approach by pouring radiolabeled particles into tanks of scallops. The university is now using the same technique with other fish.
The researchers fed the scallops 24 nm and 250 nm polystyrene particles at a dose of 15 µg per liter of water. This is equivalent to the concentration of nanoscale plastics found in the environment, the researchers say. They found that billions of particles lodged in the scallops’ intestines, kidneys, gills, and muscles. The results show for the first time that nanoplastics can be rapidly taken up by a marine organism and that in just a few hours they become distributed across most of three major organs, the researchers say.
A lack of standards in the assessment of microplastics has hampered direct comparison of studies. A host of organizations, including the European Commission’s Joint Research Centre (JRC) and the scientific instrument makers Agilent Technologies and PerkinElmer, are looking to change this situation.
Agilent says it is developing instrument software featuring standard operating protocols for quantifying and characterizing microplastics.
To this end, the firm has teamed up with Jes Vollertsen, a professor in the Department of Civil Engineering at Aalborg University. His research group has written a program that automatically analyzes Agilent’s FT-IR imaging data and presents color-coded images based on chemical identification.
PerkinElmer says it has used involvement in projects, such as its research collaboration with Greenpeace assessing microplastic pollution in Antarctica, to provide guidance for using FT-IR microscopy to assess microplastics. PerkinElmer has also created the Microplastics Scientific Network to share updates on research and regulatory activity, says Ian Robertson, a senior applications scientist for spectroscopy at the firm.
Meanwhile, the JRC is developing standard protocols for FT-IR combined with Raman spectroscopy. The approach is becoming a routine method for chemically identifying micrometer-range polymer particles, although it is currently too time consuming, says Brigitte Toussaint, project officer for the JRC. Depending on spatial resolution, analyzing a few square centimeters using this technique can take up to 24 h, Toussaint says. Another drawback of the combination is that it’s ineffective at analyzing particles below 0.5 µm, she says.
The JRC is seeking technologies that are faster and more sensitive. To identify polymer particles smaller than 100 nm, FT-IR could be combined with atomic force microscopy scanning technology, Toussaint says.
Other sensitive analytical techniques, such as X-ray photoelectron spectroscopy, may have a role in assessing microparticles as well as providing information about absorbed surface contaminants, she says, but they are complex and costly and are most appropriate for resolving specific analytical problems rather than for routine analysis.